The subject invention relates to the problem of providing a robust, compact characterization of a block of printed text which will distinguish the selected block of text from other such blocks. More particularly, it relates to the problem of estimating the robustness of algorithms for generating characterizing information descriptive of printed material. (By “robust and compact” herein is meant information which is small enough in quantity to be incorporated into postal indicia yet will identify a text block, and distinguish it from other text blocks, with sufficient reliability to deter “rubber stamp” counterfeiting; despite errors introduced by the printing and/or scanning processes.)
Postage metering systems account for postage and other values such as parcel delivery service charges and tax stamps, and print indicia representative of such values as proof of payment. To protect against counterfeiting of indicia, modern digital postage metering systems use encryption technology. The postage value and other information relating to an indicium are preferably digitally signed, or otherwise cryptographically authenticated, and the information and signature are incorporated into the digital postal indicium.
Digital postal indicia using encryption technologies are extremely secure. In general, without knowledge of the proper encryption keys, it is essentially impossible to produce a counterfeit digital indicium. However, digital indicia are subject, as are all postal indicia, to “rubber-stamp” counterfeiting when a valid indicium is scanned and reproduced on multiple mail pieces. To prevent such “rubber-stamp” counterfeiting, it is known to incorporate information from the address block of the mail piece into the postal indicium. Because space on an envelope is limited, typically only a small portion of the information in the address block will be incorporated into the indicium.
In FIG. 1, prior art mailing system 10 includes address printer controller 12, address printer 14, postage meter 16, and indicia printer 20. Address printer controller 12 receives address information from a data processing system (not shown), generates a bitmap representative of the nominal, or “pristine”, image of the address block, and controls address printer 12 to print address block A, representative of the address, on envelope E. Meter 16 receives postage information, and other information, from the data processing system. Meter 16 also receives characterizing information descriptive of block A from address printer controller 12. The information received can be either text-based or image-based. Text-based information is descriptive of the words or characters making up to the address, (e.g., ASCII code) while image-based information is descriptive of the actual printed image in the address block. Meter 16 combines the characterizing information with the postage value and other information, typically digitally signs the combination, generates a bitmap representative of an indicium including the digitally signed combination, and controls indicia printer 20 to print indicium IN on envelope E. When the mail piece is sent to a postal service location the address block can be scanned again, and the information regenerated from the scanned address block compared to information recovered from indicium IN, without the need to communicate with the remote mailing system; thus tying indicium IN to the particular mail piece. (Note that since indicium IN is cryptographically linked to the address on the mail piece, printer 20 need not be a secure printer; but can be a general purpose printer which can be controlled by other devices for other uses.) Commonly assigned, provisional application No. 60/386,868 filed Jun. 7, 2002, entitled System And Method For Mail Destination Address Information Encoding Protection And Recovery In Postal Payment in the name of Leon A. Pintsov discloses a system similar to that of the FIG. 1 using text-based characterizations of the address block.
While useful for its intended purpose, problems remain with the system of FIG. 1 and similar systems. It has proven difficult to reliably recover textual information from address blocks during the validation process using available optical character recognition (OCR) techniques. Attempts to increase the robustness of text-based systems by incorporation of additional information and/or the use of error correcting codes has resulted in undesirable increases in indicia size and computational complexity. Use of image-based characterizing systems, such as those described in the above mentioned co-pending application Ser. No. 60/386,868, has been proposed and is believed to substantially overcome some of the problems of text-based systems; however, it has proven difficult to form a priori estimates of the robustness of proposed characterizing algorithms for image-based system; forcing users to undertake extensive trial and error testing of various algorithms. This problem is exacerbated by the variation in robustness of characterizing algorithms with respect to the particular text block to be characterized. Thus, it is an object of the present invention to provide a method and system for estimating the robustness of characterizing algorithms with respect to a particular text block.